A private network is generally a closed communication network provided for carrying out communications between specified users, for example, internal users of an enterprise. Private networks improve security, efficiency, and flexibility of communications between such internal users. There are also private networks in the marketplace that provide communication service to a specific subset of public network subscribers where each private subscriber is a public network subscriber and therefore has a public network mobile identification number (MIN), for example 212600-1234. At the same time, each of these subscribers is also a private network subscriber and therefore has a private network subscriber identification number, for example 700-5678.
FIG.1 shows a block diagram of a private network having a communication link with a public network in accordance with a prior system. The private network enables wireless and wire-line communication within the private network, as well as wired communication between the private and public networks. When assurance of security is an important issue, the private network may be configured to permit access only by authorized subscribers. Private branch exchange (PBX) 102 provides an access point to the private network by the subscribers 104 and 105, and a controller 103 provides overall control of the private wireless network, including authenticating incoming calls. Controller 103, such as a wireless office service (WOS) controller provided by AT&T, functions as a PBX that controls the private network. A WOS controller is similar to a mobile switching center (MSC) 106, but on a smaller scale, and controls the private network's base station(s), communicates with the public network to authenticate calls, and also registers a subscriber when he/she becomes active. WOS controller 103 also has a signaling capability in order to interface with and control certain functions of the public network, the private PBX 102, and the private base stations. In short, WOS controller 103 provides control signaling and voice traffic management for the private wireless network.
Private networks, including wireless and wire-line networks, do not usually have a direct connection to access public network voicemail system 113. When a call to a private network subscriber (when that subscriber is registered on the private network) is not answered, private branch exchange 102 switches the call to private network voicemail system 107 to receive and store messages in a voice mailbox. Likewise, when a call to a public network subscriber goes unanswered, voice messages are routed to and stored in a voice mailbox of the public network voicemail system 113. An inconvenience encountered by subscribers having access to both a public and private network is a requirement to check his or her voice mailbox both in voicemail system 107 and in voicemail system 113 in order to retrieve all messages. This inconvenience often prevents a private network provider from offering public network voicemail to its subscribers when they are also using a private network.
Another system that provides voicemail service to private network subscribers uses an interface, such as a Primary Rate Interface (PRI) that directly connects the private network to a public network. A PRI is similar to ISDN, or T1 lines. It is a dedicated ‘voice’ line with signaling or control capability between two switches. It is, however, not necessary to use PRI in many instances since any dedicated line between the private and public networks will suffice. Because the PRI uses a dedicated line, there is usually very minimal security risk. The issue is usually a potentially prohibitive cost to run a dedicated line from an office building to an off-site voice mailbox location, especially if it is across the country. Although the PRI saves a subscriber from a need to check two voicemail systems to retrieve messages, the minimal security risk that arises by interconnecting the public and private networks still may be unacceptable to some private network providers.